In short
A Teams Direct Routing SBC is the Session Border Controller that links Microsoft Teams Phone to a carrier, SIP trunk or phone system. Microsoft supports Direct Routing only with SBCs it has certified. The SBC can run on your site, in your cloud or in a provider's cloud. Forever Systems can quote Direct Routing with the certified SBC run for you.
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What an SBC does in Direct Routing
A Session Border Controller (SBC) sits at the edge between two voice networks. In Direct Routing it stands between Microsoft's Direct Routing service and the carrier, SIP trunk or phone system on the other side.
- It carries the signalling. The SBC and Microsoft exchange call set-up messages as SIP over TLS
- It carries or steers the audio. Call audio is encrypted and passes through Microsoft's media processors, or directly between the user and the SBC where media bypass is used
- It handles the codecs. Microsoft lists the audio codecs supported between Teams and the SBC, and administrators can prioritise or restrict them on the SBC
- It is the security boundary. The SBC is identified by a name in your Microsoft 365 domain and a public trusted certificate
Which SBCs are supported for Direct Routing
Only certified ones. Microsoft says it supports Teams Phone with Direct Routing only when certified SBCs are used, and it keeps the list of Session Border Controllers certified for Direct Routing (opens in a new tab) on Microsoft Learn. The list changes, so we check it for you when we quote; with our Teams calling service the certified SBC is run for you.
Microsoft describes what certification involves:
- Joint work with each vendor on the SIP interconnection
- Tests in a third-party lab; only devices that pass are certified
- Daily tests of certified devices in production and pre-production environments
- A joint support process with the SBC vendor
Certification is granted to specific firmware versions, so the version an SBC runs matters as much as the product.
What the SBC needs
Microsoft's planning guide sets out what must be in place around the SBC:
| Requirement | What Microsoft asks for |
|---|---|
| Name | A fully qualified domain name in a verified Microsoft 365 domain. The default onmicrosoft.com domain cannot be used |
| Certificate | A public trusted certificate for that name, for secure TLS communication |
| Addressing | A public IP address that Microsoft Teams can reach, and a public DNS entry |
| Trunks | One or more connections to a carrier |
| Firewall | The Microsoft Teams signalling and media ports opened |
Teams Direct Routing requirements covers each of these, with the ports and certificate rules.
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Media bypass
By default, call audio flows through Microsoft's media processors. Media bypass shortens that path: Microsoft says the audio is kept between the SBC and the user's Teams client, with signalling still flowing through the Microsoft cloud. Microsoft recommends it where the user is in the same building or network as the SBC, and notes that the Teams client must be able to reach the SBC's public IP address.
Where the SBC can run
| Where | Who looks after it | What is on your site |
|---|---|---|
| On your premises | Your IT team or an integrator | The SBC, with its trunks and firewall rules |
| In your own cloud | Your IT team or an integrator | Nothing for the SBC itself |
| In a provider's cloud | The Direct Routing provider | Nothing |
The third row is Direct Routing as a Service, and it is how our Teams calling service works: the certified SBC, its certificate and the carrier connection are run for you. Microsoft Teams Direct Routing providers explains the model.
Contact us if you would like Direct Routing without an SBC of your own.
Is Microsoft Teams Direct Routing the right fit for you?
We will check it against your systems and requirements and recommend the right option.
Who supports the SBC
Microsoft sets the support path. If a Direct Routing issue arises, the customer contacts the SBC vendor first; the vendor investigates and, if needed, escalates to Microsoft. Microsoft asks for the vendor's investigation report when a support request is opened, and may decline requests that involve an SBC that is not certified. With a hosted service, the provider is the one who deals with the SBC vendor.
Sources (checked 11 November 2026): Microsoft Learn, "Plan Direct Routing", "Session Border Controllers certified for Direct Routing" and "Plan for media bypass with Direct Routing".
How Forever Systems helps with Teams Phone
Forever Systems can quote and set up Microsoft Teams Phone for your organisation and connect it to the phone network.
- Licence and calling check: we look at the Microsoft 365 plan you hold and recommend the Teams Phone licences and calling option that fit
- Numbers kept: we plan and manage the porting of your existing numbers
- Call flows set up: auto attendants, call queues and opening hours built and tested with you
- Works with what you use: the Teams apps on desktop and mobile
- Licensing in one place: licences can be billed monthly, with terms confirmed at quote
We work with businesses, schools, charities and public sector organisations. Pricing depends on users, licences and calling, so ask us for a quote.
Frequently asked questions
What is an SBC in Teams Direct Routing?
It is the Session Border Controller that connects Microsoft Teams Phone to a carrier, SIP trunk or phone system. It carries the call signalling, handles or steers the audio and acts as the secure boundary between the two networks.
Which SBCs are supported for Microsoft Teams Direct Routing?
Only SBCs that Microsoft has certified. Microsoft publishes the list of Session Border Controllers certified for Direct Routing on Microsoft Learn, with the firmware versions covered.
Do I have to run an SBC myself for Direct Routing?
No. Microsoft says the SBC can be run by you, your integrator or a Direct Routing as a Service provider. With a hosted service it runs in the provider's cloud and nothing is installed on your site.
What is media bypass in Direct Routing?
Media bypass keeps call audio between the user's Teams client and the SBC, where otherwise it would pass through Microsoft's media processors. Signalling still flows through the Microsoft cloud.
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